1. Field of the Invention
The present invention relates to a vibratory gyroscope, which detects a rotatory angular velocity by making use of Coriolis force generated when a vibrator rotates while vibrating and, more particularly, to a vibratory gyroscope, which permits easy adjustment of the vibratory frequency of the vibrator, stable support, and a structure ideally suited for mass production.
2. Description of the Related Art
A gyroscope for detecting a rotatory angular velocity is used for an inertial navigation system or the like for aircraft and a marine vessel; it is recently being used also for posture control in a motor-vehicle-mounted navigation system, robot or unmanned vehicle and further for a screen vibration preventing apparatus for a TV camera or video camera.
Gyroscopes suited for use in these various fields are required to be compact, and attention is now focused on a vibratory gyroscope.
FIG. 28 shows a basic structure of this type of vibratory gyroscope. This vibratory gyroscope has a column-shaped vibrator 1 made of constantly elastic alloy (elinvar), to which a driving piezoelectric element 2 and a detecting piezoelectric element 3 are attached. When the vibrator 1 is rotated around an axis O while applying bending vibration to the vibrator 1 in the direction of axis x by the driving piezoelectric element 2. Coriolis force works in the direction of axis y. The bending vibration in the direction of axis y applied to the vibrator 1 by the Coriolis force is detected as a voltage through the piezoelectric element 3.
If the mass of the vibrator 1 is taken as m, the vibration velocity of the vibrator 1 in the direction of axis x given by the driving piezoelectric element 2 as v (vector value), and the angular velocity centering around axis O as .omega. (vector value), then Coriolis force F (vector value) will be as follows: EQU F=2 m(v x .omega.)(x: Vector product)
Coriolis force F is proportional to the angular velocity .omega.. The distorted vibration of the vibrator 1 in the direction of axis y caused by the Coriolis force F is converted into a voltage through the detecting piezoelectric element 3, and the angular velocity .omega. is determined from the detected voltage.
The gyroscope shown in FIG. 28, however, uses expensive constantly elastic metal, which is machined into a column shape; therefore, the yield of the material is low and the machining cost is high because of the need of machining into a column shape with high accuracy. Further, in this type of gyroscope, the resonance frequency at the time when the vibrator 1 is bent and vibrated by the driving piezoelectric element 2 must be adjusted. Accordingly, a part of the column-shaped vibrator 1 must be shaved for the adjustment, making the adjusting work extremely complicated.
The inventors of the present invention, therefore, studied a conventional tuning fork, which employs a vibrator 4 made of a plate-shaped constantly elastic metal as shown in FIG. 29. This gyroscope has a slit 4a formed at the center of the distal end of the vibrator 4, the plate being split into two pieces, namely, elastic arms 4b and 4c. As shown in FIG. 30(A), the piezoelectric element is used to vibrate the elastic arms 4b and 4c in the direction of the plate surfaces at a specific resonance frequency. The amplitude of the vibration of the elastic arm 4b is in the opposite phase from that of the elastic arm 4c at a given point, the phases being indicated by a +x direction and a -x direction. With such a vibration applied, when the vibrator 4 is given a rotation around the axis O, the elastic arms 4b and 4c develop deformation in the directions of +y and -y due to Coriolis force as shown in FIG. 30(B). The angular velocity .omega. can be determined by detecting the deformation through the detecting piezoelectric element and converting it into a voltage.
However, the vibratory gyroscope using the plate-shaped, conventional tuning fork type vibrator 4 shown in FIG. 29 and FIG. 30 presents the following problems:
(1) In the two-tine tuning fork type, the two elastic arms 4b and 4c must be trimmed separately to adjust the resonance frequency for driving, thus leading to complicated resonance frequency adjustment work. In addition, there is a fear of shaping the elastic arms 4b and 4c asymmetrically while making the adjustment; asymmetrical elastic arms 4b and 4c cause a torsion in the vibrator 4 or a vibration node at the asymmetrical point, preventing well-balanced and highly accurate detection of the deformation by Coriolis force shown in FIG. 30(B). PA1 (2) In the conventional tuning fork, when Coriolis force causes the elastic arms 4b and 4c to develop distorted vibration in a y direction, the nodal lines of the vibration appear at points (a) and (b). Hence, the vibrator 4 needs to be cantilevered by a support bar 5, for example, at the center on the trailing end, limiting the support structure. The cantilever support using the support bar 5 is unstable in mechanical support strength, causing the vibrator 4 to be susceptible to external vibration.